Method for plant monitoring with a field bus of process automation technology

ABSTRACT

A method for plant monitoring with a fieldbus of process automation technology, wherein a plurality of field devices communicate with a process control unit and a plant monitoring unit The method steps are carried out as follows: the regular, process-control, data traffic on the fieldbus is monitored by the plant monitoring unit; an examination of the telegrams of the regular data traffic for information indicating a diagnostic event at one of the field devices is performed; and in case a telegram is detected having an indication of a diagnostic event, the plant monitoring unit requests further diagnostic information from the pertinent field device.

TECHNICAL FIELD

The invention relates to a method for plant, or installation, monitoringwith a field bus of process automation technology, as such method isdefined in the preamble of claim 1.

BACKGROUND DISCUSSION

In automation technology, field devices are often used, to serve formeasuring and/or influencing process variables. Examples of such fielddevices are fill-level measuring devices, mass-flow measuring devices,pressure and temperature measuring devices, etc., which, as sensors,register the corresponding process variables, fill-level, flow (e.g.flow rate), pressure and temperature.

Field devices serving as actuators, to influence process variables,include, e.g., valves for controlling flow of a liquid in a section ofpipeline or pumps for controlling fill level in a container.

A large number of such field devices are manufactured and sold by thefirm, Endress+Hauser.

As a rule, field devices in modern manufacturing plants are connectedvia communication systems (HART, Profibus, Foundation Fieldbus, etc.)with superordinated units (e.g. control systems or control units). Thesesuperordinated units serve, among other things, for process control,process visualizing, process monitoring, as well as for tasks such ascommissioning and other servicing of field devices.

Also falling under the heading “field devices” are, in general, suchunits (e.g. remote I/Os, gateways, linking devices) as are directlyconnected to a fieldbus and serve for communication with thesuperordinated units.

Fieldbus systems can be integrated into company networks. In this way,process and field device data can be accessed from different areas of anenterprise.

For worldwide communication, company networks can be connected also withpublic networks, e.g. the Internet.

The servicing of field devices requires corresponding operatingprograms. These operating programs can run independently in thesuperordinated units (e.g. FieldCare, Endress+Hauser; Pactware; AMS,Emerson; Simatic PDM, Siemens) or they can be integrated into controlsystem applications (e.g. Simatic PCS7, Siemens; ABB Symphony; Delta V,Emerson). Besides control system applications, also operating programs,in part, already exhibit functionalities as regards plant monitoring(asset management).

A user places, in principle, two completely different requirements onfieldbus systems. One of these is process control, and the other isplant monitoring, or plant visualizing.

In the case of the fieldbus system PROFIBUS®, process control occurs viaa cyclic data transfer. In such case, field devices exchange measuredvalues at regular intervals with a process control unit (Controller),which generates corresponding control commands, e.g. for the pertinentactuators. As is known, in the case of PROFIBUS, communication betweenprocess control unit and field device is done using theMaster-Slave-principle, wherein the process control unit functions asmaster and the field devices as slaves. Control of bus access is managedby the master, which sends control commands to the individual fielddevices via polling telegrams. The field device is permitted to transmitmeasured values to the master in a response telegram only after it hasfirst received a polling telegram. The sequence of polling telegram andresponse telegram is executed by the master in time sequence with eachof the slaves associated with it. The time until, in this way, each ofthe slaves associated with the master has been processed is referred toas the cycle time. Following the end of a cycle, the master then beginsa new cycle. Process control systems are microprocessor-based,automation devices, whose control functionality is specified byautomation software produced by automation personnel in the course of anengineering procedure and executed in the automation device in realtime.

Programs or parts of programs having functionalities as regards plantmonitoring are referred to in the following as asset-management-systems.These serve for processing device information for monitoring andoptimizing device- and plant-states. The communication of data forasset-management purposes is done, as a rule, in the acyclic datatraffic, for which a certain time interval is available between twosucceeding cycles. The updating of data for purposes of asset-managementhappens, compared with the cyclic data traffic, in which an updatingoccurs after each cycle time, markedly slower.

Visualizing systems present the current parameters of the process on auser interface. Frequently, for the visualizing, besides the numericalvalues of a process variable and its units, also changed graphicalsymbols, such as dials, bars or trend charts, are used. Visualizingsystems draw the data, most often, from process control systems. Thevisualizing system is, in the context of a user interface, also capableof influencing certain variables in the control system, which, in turncan itself have an influence on the course of the control program or theprocess.

Since process control tasks have precedence, the time interval availablefor the acyclic data traffic is markedly shorter than the time intervalfor the cyclic traffic.

As regards diagnostic data, one distinguishes between event-dependent,diagnostic data and diagnostic data read out only upon request e.g. ofan asset-management-system. In the case of the fieldbus system,PROFIBUS, event-dependent, diagnostic data are bound to thecommunication partner cyclically communicating with the slave devicesassigned to it (PROFIBUS Master Class 1).

This assures that a process control unit having cyclic data exchangewith the slave devices reacts in near time to the diagnostic results. Anasset-management-system connected with a control system application canbe prompted by such application to fetch acyclic, diagnostic data.Therewith, the advantages of the event-dependent diagnosis (shortreaction time) can be coupled with the desire for detailed information(additional, diagnostic data, which are communicated acyclically). Whilethe diagnostic data communicated in place of the process data are ofBoolean nature (to each bit corresponds a piece of diagnostic data,which can be identified by the device), the acyclically transmitted,diagnostically relevant data can include e.g. the degree of wear of aprobe or the degree of fouling of the measuring device.

Proprietary solutions are known for the combination of process controland asset-management-system (for example, SIMATIC PCS7, of the firm,Siemens).

An asset-management-system independent of the process control can onlyrequest diagnostic data in the acyclic data traffic. Since, in thiscase, the asset-management-system is not informed of diagnostic eventsby a process control, it is necessary that diagnostic data be regularlyrequested, in order that diagnostic events can even be noticed by theasset-management-system.

Especially in the case of plants having a significant number ofinstalled field devices and a multiplicity of diagnostically relevantparameters to be monitored, it is a fact that the updating of theseparameters in the asset-management-system takes a very long time, sothat long reaction times result. These long reaction times are verydisadvantageous, especially in the case of critical diagnostic events.The long reaction times can even compromise the ability of the assetmanagement systems to function.

The terminology “diagnostic event” is meant to include not onlydiagnostic reports from field devices but also issuance of alarms.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method for plant monitoringwith a fieldbus of process automation technology not having the abovediscussed advantages, while possessing a highest possible measure ofindependence from the process control and, in spite of this, reacting todiagnostic events as quickly as possible.

This object is achieved by a method comprising the steps of: monitoringby a plant monitoring unit regular, process-control, data trafficcarried on a fieldbus to which a plurality of field devices areconnected; examining telegrams of the regular data traffic forinformation indicating a diagnostic event at one of the field device;and, in case of a telegram with an indication of a diagnostic eventbeing detected, requesting by the plant monitoring unit furtherdiagnostic information from such field device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail on the basis of anexample of an embodiment presented in the drawing, the figures of whichshow as follows:

FIG. 1 is a network of process automation technology; and

FIG. 2 is a timing diagram of a Master-Slave communication.

DETAILED DISCUSSION

FIG. 1 shows a network of process automation technology. Attached to afieldbus FB are a plurality of field devices F1, F2, F3 and F4.Additionally connected to the fieldbus FB are a controller C (forexample, FieldController of the firm, Endress+Hauser) and a gateway G(for example, FieldGate of the firm, Endress+Hauser). Controller C isconnected with a computer unit CU1 serving as a visualizing system.Gateway G is connected with a computer unit CU2, which serves forobserving field devices.

Field devices F1 to F4 are configured as slaves. Controller C isconfigured as Master Class 1 and Gateway G as Master Class 2. Serving asprocess control unit is controller C, which cyclically sends output datato the individual field devices and receives output data from theindividual field devices.

Serving as plant monitoring unit is the Gateway G, which communicatesacyclically with the field devices.

FIG. 2 shows, schematically, a timing diagram for communication betweencontroller C (Master) and field device F1 (Slave).

The Master sends, normally in cyclic data traffic, a polling telegram(request) to the Slave, and the Slave answers with a response telegram(response) with low priority (Data_Exch).

The priority is shown in the Profibus telegram in the frame controlbyte.

In the case of a diagnostic event in the slave, the priority of theresponse telegram is changed from “low” to “high”. As soon as a responsewith high priority is sent from the field device, in the next datatraffic from the master, a Slave_Diag request is issued, instead of aData_Exchange request, so that the Master is now requesting diagnosticdata from the slave, instead of process data.

At the point in time T1, such a diagnostic event “(Diagnostic case)”occurs. To the request of the Master, the slave responds with a responsewith priority “high”.

Due to this information indicating a diagnostic event in the fielddevice, the Master sends a request (Slave_Diag) and the Slave answerswith a response (Slave_Diag). This response contains special diagnosticdata of the slave.

Thereafter, the cyclic data traffic is resumed. At the point in time T2,the diagnostic event “diagnostic case ended” or “change of diagnosticdata” enters. In order that the current diagnostic data can betransmitted to the Master, the slave sends anew a response with highpriority, which, in turn, prompts the Master to send a request(Slave_Diag), whereupon the slave responds with a response (Slave_Diag).

Only an asset management system integrated in the master can accessthese diagnostic data present in the master, or bring about that themaster activates acyclic data access, in order to obtain additionaldiagnostic data from the field device. These accesses are then executedvia read requests.

An asset management system independent of the control system, asintegrated, in the present case, in the gateway G, can, however, onlyobtain diagnostic data, when it obtains, as Master Class 2, on the basisof the occurrence of a diagnostic event, the right to transmit, in orderso to obtain diagnostic-relevant data via acyclic communication.

The method of the invention will now be explained in greater detail.Gateway G monitors, or taps (in the sense of wiretapping), as plantmonitoring unit, the regular data traffic on the fieldbus FB. Thisregular (cyclic) data traffic serves essentially for process control.

In the Gateway G, an examination of this data traffic for informationindicating the entering of a diagnostic event at one of the fielddevices occurs. A diagnostic event can be e.g. a malfunction of thefield device per se or, however, also the measuring of a surroundingtemperature which is too high (Alarm). Thus, the individual telegrams ofthe regular data traffic are analyzed as to whether a response telegramof a slave is being transmitted with high priority.

In case a telegram of a slave is detected having an indication of adiagnostic event, gateway G requests further diagnostic information fromthe pertinent field device.

An essential advantage offered by the method of the invention is thatthe asset-management-system provided in the gateway G does not have toregularly query each individual field device for diagnostic informationin acyclic traffic, but, instead, only when a concrete indication of adisturbance is present.

In this way, also an asset-management-system independent of a processcontrol can detect diagnostic cases quickly and reliably and introduceappropriate measures. An opportunity is provided therein to representthe diagnostic event for the user or to enter it into a database with acorresponding date stamp. Also E-Mails or SMS text messages containinginformation corresponding to the diagnostic event can be sent from theasset-management-system to responsible persons.

The invention can be applied both in the case of the Profibus fieldbussystem and also in that of Foundation Fieldbus. To adapt FIG. 1 to theFoundation Fieldbus system, remove the designations Master Class 1 andMaster Class 2 and replace the label Profibus DP with FoundationFieldbus.

The invention relates not only to the detection of diagnostic events,but, instead, extends to the observation of the current process data ofa certain one or all connected slaves as such data is transmittedcyclically to the pertinent master, without the bus traffic beingcompromised. The process data of a slave are now made available to avisualizing system, or to an asset management system, or to acommunication participant of another communication system, without theplant monitoring unit G itself actively participating in the buscommunication therefor. The plant monitoring unit is, in this case, itis true, connected to the fieldbus FB, but it is not configured as a busparticipant. It only monitors the bus traffic and lets the telegramsproceed.

The telegrams are examined in the plant monitoring unit as to whether atelegram is one of the cyclic data exchange. In case such is true, thecontent of the telegram is stored together with the followinginformation: destination address of the telegram and source address ofthe telegram.

If the destination address is the master address, then the data islabeled as “input data from the slave with source address”. If, incontrast, the source address is the master address, then the data islabeled as “output data to the slave with the destination address”.

The storage can be done in a permanent memory that stores all telegrams.Alternatively, the storage can be done in a circular, or ring, buffer,which stores a certain amount of data, or in a memory which overwrites aprevious telegram with a new telegram having the identicalsource/destination address.

The detected process data, together with the information concerningdestination/source address, are made available to a visualizing system.The visualizing system can be part of the plant monitoring unit or partof the computer unit R2. The data can be transmitted to the visualizingsystem via a proprietary communication protocol or an open communicationprotocol.

The detected process data can also be made available to an assetmanagement system, together with the information concerningdestination/source address.

Alternatively, the detected process data, together with the informationconcerning destination/source address, can be made available to acontrol system. The detected process data can then be utilized in theautomation software, in order to initiate reactions of the controlsystem for influencing the process.

The detected process data can also be made available via an interface,e.g. a PROFINET I/O-interface in the sense of a PROFINET I/O-device,provided in the plant monitoring unit G. In this way, the process datadetected in the PROFIBUS-DP-system are transmitted into a PROFINETIO-system.

The invention claimed is:
 1. A method for plant monitoring a pluralityof field devices connected with a fieldbus of process automationtechnology, with a process control unit and a plant monitoring unit, themethod comprising the steps of: connecting the process control unit andthe plant monitoring unit to the fieldbus; generating regular datatraffic using the process control unit by cyclically sending output datato the individual field devices and receiving output data from theindividual field devices; issuing telegrams of the regular data traffic;tapping by the plant monitoring unit the regular data traffic generatedby the process control unit, examining by the plant monitoring unit theissued telegrams of the regular data traffic for information indicatinga diagnostic event at one of the field devices; and requesting, when atelegram issued by a field device and detected by the plant monitoringunit, which telegram indicates a diagnostic event, by the plantmonitoring unit via acyclic traffic further diagnostic information fromsuch field device, wherein: acyclic data traffic occurs during a certaintime interval which is available between two succeeding cycles ofregular data traffic.
 2. The method as claimed in claim 1, wherein: agateway that is connected to the field bus fieldbus serves as plantmonitoring unit which communicates acyclically with the field devices.3. The method as claimed in claim 2, wherein: an asset management systemindependent of the process control system unit is integrated in thegateway.
 4. The method as claimed in claim 2, wherein: the examining forindication indicating the entering of a diagnostic event at one of thefield devices occurs in the gateway.
 5. The method as claimed in claim1, wherein: increased priority of a telegram sent from a field deviceserves for indicating a diagnostic event.
 6. The method as claimed inclaim 1, wherein: a diagnostic request from the process control unit tothe field device serves for indicating a diagnostic event.
 7. The methodas claimed in claim 1, wherein: the plant monitoring unit itself is notactively participating in the bus communication therefore.
 8. The methodas claimed in claim 1, wherein: the plant monitoring unit is notconfigured as a bus participant.
 9. The method as claimed in claim 1,wherein: a gateway that is connected to the field bus serves as plantmonitoring unit.
 10. A method for plant monitoring with a fieldbus ofprocess automation technology, wherein a plurality of field devicescommunicate via the fieldbus with a process control unit, wherein aplant monitoring unit is connected with the fieldbus, the methodcomprising the steps of: tapping by the plant monitoring unit regulardata traffic, related to process-control, on the fieldbus, whereas theprocess control unit cyclically sends output data to the individualfield devices and receives output data from the individual fielddevices, wherein the regular data traffic consists of cyclic datatraffic, examining by the plant monitoring unit telegrams as to whetherthe tapped data are cyclic telegrams; in the case of cyclic telegrams,storing the content of the telegram together with the telegramdestination address and the telegram source address; and forwarding thecontent of the telegram together with the information concerningdestination/source address to a visualizing system, or an assetmanagement system, or a communication participant of anothercommunication system; examining by the plant monitoring unit the issuedtelegrams of the regular data traffic for information indicating adiagnostic event at one of the field devices; and requesting, when atelegram issued by a field device and detected by the plant monitoringunit, which telegram indicates a diagnostic event, by the plantmonitoring unit via acyclic traffic further diagnostic information fromsuch field device; wherein acyclic data traffic occurs during a certaintime interval which is available between two succeeding cycles ofregular data traffic.
 11. The method as claimed in claim 10, wherein:the plant monitoring unit itself is not actively participating in thefieldbus communication therefore.
 12. The method as claimed in claim 10,wherein: the plant monitoring unit is not configured as a busparticipant.
 13. The method as claimed in claim 10, wherein: a gatewaythat is connected to the field bus field bus serves as plant monitoringunit.